1. Field of the Invention
The present invention generally relates to a device for indicating the wear of a friction clutch which is located in the drive train of a motor vehicle between its engine and its transmission, which friction clutch, including a release system which can be moved by an actuator mechanism between two defined limit positions relative to the transmission, is enclosed by a housing which is stationary relative to the transmission.
2. Background Information
WO 95/09311 discloses a device of the type described above in which an indicator element, which indicator element is coupled to the release piston of a release piston cylinder unit oriented coaxial to the clutch, projects outward through an opening in the housing. The back-and-forth movement of the release piston is indicated on the outside of the housing. However, the magnitude of the movement of the display element does not indicate directly, or not without a more exact measurement, whether the clutch is completely worn or not.
Friction clutches are used in motor vehicles as starter clutches or as lock-up clutches for hydraulic torque converters and are located between the internal combustion engine and the downstream transmission of the motor vehicle. For maintenance purposes, the service technician must be able to quickly and easily determine the extent to which the clutch is worn, even under the less-than-favorable and cramped conditions it which the clutch is installed, and in which conditions clear and unobstructed visibility is difficult. In particular, the technician must be able to determine whether the clutch has become worn to the point where it must be replaced. The device described in WO 95/09311 indicates only the relative wear condition. To determine whether the clutch has or has not reached the maximum allowable wear limit, the service technician must either measure the inclination of the indicator element relative to the surface of the housing, although that can be extremely difficult given the cramped and inaccessible conditions in which the clutch housing is installed, or the wear must be indicated by using an electrical display which is connected to the indicator element. The electrical indicator is complex and expensive.